Surprising Science Demonstrations?

An anonymous reader writes: "I have been called upon to conduct some science workshops for children of various ages, and I'm looking for some good demos. In particular, I've found that demos are most effective at getting students to think when they give a surprising or unexpected result, such as the classic two-slit experiment (or, for the extreme crowd, demonstrating the Leidenfrost effect by sticking one's hand into a vat of molten lead [PDF]). I'd like the Slashdot crowd's suggestions." Please don't do the lead one.

Comments

Baking soda and vinegar

[npietraniec]

Anything that explodes is cool. Baking soda and vinegar, Sodium and water, Magnesium and fire, drano and tinfoil... :)

Are these demos effective?

[Goonie]

This is slightly OT, but I've always wondered about how effective these shows are in getting kids interested in science. Sure, they enjoy them greatly when they go, but do they actually care about why all this is happening, and how people figured out all this stuff?

How do you get people enthused about the actual process of science - coming up with hypotheses, figuring out how to test them, analysing the results, and so on?